Method of using a mud motor

ABSTRACT

This application is directed to methods of using pressure balanced mud motors. The mud motor includes a power section to rotate a passageway housing and propel fluid through a passageway disposed in the passageway housing. The mud motor can also include a roller bearing assembly and a drive shaft assembly to improve the life and efficiency of the pressure balanced mud motor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication having U.S. Ser. No. 14/104,276, filed Dec. 12, 2013, whichclaims the benefit under 35 U.S.C. 119(e). The disclosure of which ishereby expressly incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

The present invention relates to a mud motor used in oil and gasoperations that is pressure balanced.

2. Description of the Related Art

Standard sealed mud motors typically have radial bearings/assembliesthat are exposed to well bore fluids. The fluid that operates the sealedmud motor must pass across the bearing assemblies and out of the sealedmud motor. Typically, the bearing assemblies have seals that preventpumped fluid from contaminating any grease or oil used in the bearingassemblies. As fluid flows through the sealed mud motor and across theseals and bearing assemblies, a pressure drop occurs between upper andlower seals associated with the bearing assemblies due to the frictionloss associated with fluid flowing through the sealed mud motor. Thispressure drop can cause the seals to leak, allowing drilling fluid toenter the bearing assemblies and cause premature failure of the bearingassemblies.

Accordingly, there is a need for a sealed mud motor that can balance thepressure drop across the seals/bearing assemblies caused by the frictionof the fluid flowing through the sealed mud motor.

SUMMARY OF THE DISCLOSURE

The present disclosure is directed to a method of using a pressurebalanced mud motor. The mud motor includes an outer housing having anupper portion and a lower portion and a power section disposed withinthe housing for rotating a passageway housing in response to fluid flowthrough the power section. The mud motor also includes a passagewaydisposed in the passageway housing where a small fluid volume is createdbetween the passageway housing and the outer housing and a bearingassembly for facilitating the rotation of the passageway housing.Furthermore, the mud motor includes a hydraulic apparatus for balancinga pressure drop experienced across the bearing assembly due tofrictional flow of fluid through the passageway.

The present disclosure is also directed to a method of using a pressurebalanced mud motor that includes a power section disposed within ahousing for rotating a passageway housing, the power section having arotor and a drive shaft assembly. The drive shaft assembly of the mudmotor includes a shaft having a first end and a second end fortransferring rotation of the rotor to the passageway housing, the firstend having a depression slot disposed thereon and a socket elementsupported by the rotor and adapted to receive the first end of theshaft. The drive shaft assembly also includes at least one elongated pinhaving a first end and a second end, the first end disposed in at leastone pin opening in the socket element and the second end engaging thedepression slot disposed on the first end of the shaft.

The present disclosure is also directed to a method of using a apressure balanced mud motor that includes a roller bearing. The rollerbearing of the mud motor includes a roller cage having an inner ring, aplurality of extension elements extending therefrom and an outer edge,each pair of adjacent extension elements cooperating to form a pluralityof bearing seats and a plurality of rollers disposed in each bearingseat. The roller bearing also includes a retaining ring disposed aroundthe outer edge of the roller cage to maintain the rollers in the bearingseats, the retaining ring and the outer edge of the roller cage having atapered interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a downhole mud motor constructed inaccordance with the present disclosure.

FIG. 2A is a cross-sectional view of a portion of the downhole mud motorconstructed in accordance with the present disclosure.

FIG. 2B is a cross-sectional view of another embodiment of a portion ofthe downhole mud motor constructed in accordance with the presentdisclosure.

FIG. 3 is a cross-sectional view of another portion of the downhole mudmotor constructed in accordance with the present disclosure.

FIG. 4 is an exploded view of a portion of the downhole mud motorconstructed in accordance with the present disclosure.

FIG. 5 is a cross-sectional view of another embodiment of a portion ofthe downhole mud motor constructed in accordance with the presentdisclosure.

FIG. 6 is an exploded view of another portion of the downhole mud motorconstructed in accordance with the present disclosure.

FIG. 7 is a perspective view of the portion of the downhole mud motorshown in FIG. 6 and constructed in accordance with the presentdisclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to a mud motor 10 used in downhole oiland gas operations that substantially reduces a pressure drop (orpressure differential) across the portions of the mud motor 10 caused bythe friction of fluid (e.g., mud, drilling fluid, drilling mud, etc.)flowing therethrough. The present disclosure is also directed to amethod of using this mud motor while maintaining a substantiallybalanced pressure drop across various portions of the mud motor. Shownin FIG. 1, the mud motor 10 includes an upper portion 12, a lowerportion 14 and a housing 16 for encapsulating various parts of the mudmotor 10.

The upper portion 12 includes a power section 18 for driving/forcing thefluid through the mud motor 10 and rotating the various parts of the mudmotor 10 encapsulated in the housing 16 and a drive shaft assembly 20for transferring the rotation produced by the power section 18 to othercomponents disposed in the lower portion 14 of the mud motor 10.

The lower portion 14 of the mud motor 10 includes a passageway 22 andpassageway housing 24 disposed therethrough to transfer fluid drivenfrom the power section 18 out of a lower end 26 of the mud motor 10, abearing assembly 28 for facilitating the rotation of the passagewayhousing 24 and a hydraulic apparatus 30 for reducing the pressure dropacross the passageway 22 and the bearing assembly 28. Fluid is passedfrom the power section 18 into an upper annulus area 32 in the upperportion 12 of the mud motor 10. The fluid is then transported into thepassageway 22 from the upper annulus area 32 via a conduit 34 disposedin the passageway housing 24.

The power section 18 can be any device known in the art for drivingfluid through the mud motor 10 and rotating various components in themud motor 10. In one embodiment, the power section 18 can include arotor 36 and stator 38 that operate as a moineau-type motor. The rotor36 in a moineau-type motor rotates and orbits within the stator 38. Thedrive shaft assembly 20 is adapted to compensate for the orbiting androtating motion of the rotor 36 within the power section 18 and transferonly the rotating motion to the passageway housing 24 in the lowerportion 14 of the mud motor 10.

In one embodiment, the bearing assembly 28 includes at least one bearing40 for facilitating the rotating of the passageway housing 24, alubrication fluid housing 42 for containing a lubricating fluid supplyfor use with the mud motor 10, and a first sealing element 44 disposedadjacent to one end of the lubrication fluid housing 42 and a secondsealing element 46 disposed adjacent to the other end of the lubricationfluid housing 42. The sealing elements 44 and 46 prevent drilling fluidfrom entering the lubrication fluid housing 42 and lubrication fluidfrom exiting the lubrication fluid housing 42. In another embodiment,the bearing assembly 28 includes a floating piston 48 to eliminatepressure drop across the bearing assembly 28 due to hydrostaticpressure.

The pressure drop generated across the bearing assembly 28 and/or thepassageway 22 from the friction of the fluid passing through thepassageway 22 can be high enough such that the sealing elements 44 and46 can leak or wear excessively. The pressure drop can allow drillingfluid to enter the lubrication fluid housing 42 or allow lubricatingfluid to exit the lubrication fluid housing 42. Either one of thesepotential occurrences can be detrimental to the operation of the mudmotor 10.

The lower portion 14 of the mud motor 10 includes a small annulus area50 disposed between the passageway housing 24 and the housing 16 where asmall fluid volume is created. The small annulus area 50 can containsmall amounts of fluid that has leaked off from the fluid that flowsfrom the upper annulus area 32, through the conduit 34 and into thepassageway 22. The small amount of fluid in the small annulus area 50 isin fluid communication with the first sealing element 44. Due to thefluid communication between the small annulus area 50 and the firstsealing element 44, the first sealing element 44 is exposed to pressureequivalent to the pressure drop generated across the bearing assembly 28and the passageway 22. The pressure drop can be either measured ordetermined based upon the length and size (diameter) of the passageway22 and the desired flow rate of fluid to be passed through the mud motor10.

Shown in more detail in FIGS. 2A and 2B, the hydraulic apparatus 30 canbe any device, or combination of devices that can hydraulically negate,or substantially negate, the pressure experienced by the first sealingelement 44 due to the pressure drop generated from the friction of thefluid flowing through the passageway 22. In one embodiment, thehydraulic pressure drop across the bearing assembly 28 (or other partsof the mud motor) due to friction of the fluid flowing through thepassageway 22 is less than about 25 psi. In another embodiment, thehydraulic pressure drop across the bearing assembly 28 (or other partsof the mud motor) due to friction of the fluid flowing through thepassageway 22 is less than about 5 psi. In yet another embodiment, thehydraulic pressure drop across the bearing assembly 28 (or other partsof the mud motor) due to friction of the fluid flowing through thepassageway 22 is less than about 0 psi.

In one embodiment, the hydraulic apparatus 30 includes a housing 52disposed within the passageway housing 24, a nozzle 54 disposed withinthe housing 52 and in fluid communication with the passageway 22, adiffusing element 56 disposed adjacent to the nozzle 54 and a port 58disposed in the housing 52 which fluidically connects the small annulusarea 50 with other components of the hydraulic apparatus 30.

The nozzle 54 includes a first end 60 in fluid communication with thepassageway 22 and a second end 62 in fluid communication with thediffusing element 56. The nozzle 54 has a cross-sectional area (thecross-sectional area referred to herein for the nozzle 54 isperpendicular to the direction of the flow of fluid through the nozzle54 and the passageway 22) that increases (divergent) or decreases(convergent) across a portion of the nozzle 54 in the direction towardthe lower end 26 of the mud motor 10. In one embodiment, thecross-sectional area of the nozzle 54 is substantially circular-shaped.The amount the cross-sectional area of the nozzle 54 increases ordecreases over a given length of the nozzle 54 can be predetermined anddesigned based upon the size of the mud motor 10 and the flow rate offluid passing through the mud motor 10. Additionally, the beginning andending cross-sectional area of the nozzle 54 can be predetermined anddesigned based upon the flow rate of fluid through the mud motor 10 andthe size of the mud motor 10. Furthermore, the nozzle 54 is designed andsized responsive to the differential pressure across the bearingassembly 28 and the first and second sealing members 44 and 46 caused bythe frictional flow of the fluid through the passageway 22.

In another embodiment, the nozzle 54 includes an annulus 64 disposedbetween an outside portion 66 of the nozzle 54 and an inner portion 67of the housing 52. The annulus 64 is in fluid communication with theport 58 and the diffusing element 56. The annulus 64 allows fluid drawnfrom the small annulus area 50 to be pulled/pushed into the diffusingelement 56 without disrupting the flow from the passageway 22 into thenozzle 54. In another embodiment, the port 58 can be disposed in thehousing 52 such that the port 58 is in fluid communication with thesmall annulus area 50 and the diffusing element 56.

The port 58 can be shaped, sized and designed to work with the othercomponents of the hydraulic apparatus 30 so that the fluid in the smallannulus area 50 is pulled therefrom at a rate that reduces the pressureon the first sealing element 44 an amount that is substantially equal tothe pressure drop across the bearing assembly 28 due to the friction ofthe fluid flowing through the passageway 22.

The diffusing element 56 includes a first end 68 in fluid communicationwith the nozzle 54 and a second end 70 in fluid communication with thepassageway 22. The diffusing element 56 can have a cross-sectional area(the cross-sectional area referred to herein for the diffusing element56 is perpendicular to the direction of the flow of fluid through thediffusing element 56 and the passageway 22) that is convergent,divergent and/or substantially constant across portions of the diffusingelement 56. In one embodiment, the cross-sectional area of the diffusingelement 56 is substantially circular-shaped. The amount thecross-sectional area of the diffusing element 56 decreases or increasesover a given length of the diffusing element 56 can be predetermined anddesigned based upon the size of the mud motor 10 and the flow rate offluid passing through the mud motor 10. Additionally, the beginning andending cross-sectional area of the diffusing element 56 for apreselected length of the diffusing element 56 can be predetermined anddesigned based upon the flow rate of fluid through the mud motor 10 andthe size of the mud motor 10. Furthermore, the diffusing element 56 isdesigned and sized responsive to the differential pressure across thebearing assembly 28 and the first and second sealing members 44 and 46caused by the frictional flow of the fluid through the passageway 22.

In one embodiment, the first end 68 of the diffusing element 56 issubstantially the same size as the second end 62 of the nozzle 54. Inanother embodiment, the first end 68 of the diffusing element 56 hassubstantially the same diameter of an outer portion 72 of the annulus 64disposed about the nozzle 54. Thus, the second end 62 of the nozzle 54is smaller in size than the first end 68 of the diffusing element 56.The depth of the annulus 64 (i.e., the difference in the radius of thesecond end 62 of the nozzle 54 and the radius of the first end 68 of thediffusing element 56) can be designed based upon the flow rate of thefluid through the mud motor 10 and the size of the other components(nozzle, diffuser element, passageway, etc.) in the mud motor 10.

In another embodiment of the present disclosure, a hole 74 (or fluidpassage) is disposed in the passageway housing 24 that fluidicallyconnects a lower portion 75 of the passageway 22 with the second sealingmember 46 (or downhole side of the bearing assembly 28) of the bearingassembly 28. The hole 74 allows the second sealing element 46 toexperience the same fluid pressure as the first sealing element 44 withthe exception of the frictional pressure drop across the bearingassembly 28 due to the fluid flowing through the passageway 22.

Fluid flow through the nozzle 54 causes the pressure in port 58 todecrease relative to the rate of flow of the fluid through the nozzle54. The diameter of the nozzle 54 is sized to a value that will causethe pressure of the fluid in port 58 to be substantially equal to thepressure of the fluid in hole 74. When the pressure of the fluid in port58 and the pressure of the fluid in hole 74 are substantially equal,then the differential pressure across the bearing assembly 28 and thefirst and second sealing elements 44 and 46 is balanced.

In yet another embodiment of the present disclosure shown in FIGS. 3-4,the drive shaft assembly 20 includes a shaft 76 for transferring therotation of the rotor 36 to the passageway housing 24, a socket element78 connected to the rotor 36 (or connected to other components connectedto the rotor 36) for receiving a first end 80 of the shaft 76 and aconnector 82 disposed at least partially around the shaft 76 andsupported by (or connected to) the socket element 78 for assisting inthe retention of the shaft 76 in the socket element 78. The drive shaftassembly 20 also includes at least one pin element 84 for engaging thesocket element 78 and the shaft 76 to assist in the transfer of rotationof the rotor 36 to the shaft 76. The drive shaft assembly 20 can alsoinclude a retaining element 86 disposed around the shaft 76 and adjacentto the connector 82 to secure the connector 82. The retaining element 86can also include openings 87 disposed therein to permit access to toolsto allow assembly and disassembly of the drive shaft assembly 20.

In another embodiment, the shaft 76 of the drive shaft assembly 20 alsoincludes a second end 88 that can be connected to the passageway housing24 to rotate the passageway housing 24. The drive shaft assembly 20 canalso include a second connector 90 disposed at least partially aroundthe shaft 76 and supported by (or connected to) the passageway housing24 and at least one second pin element 92 for engaging the passagewayhousing 24 and the second end 88 of the shaft 76 to assist in thetransfer of rotation of the shaft 76 to the passageway housing 24. Thedrive shaft assembly 20 can also include a second retaining element 94disposed around the shaft 76 and adjacent to the second connector 90 tosecure the second connector 90. The retaining element 94 can alsoinclude openings 95 disposed therein to permit access to tools to allowassembly and disassembly of the drive shaft assembly 20.

In one embodiment, each end 80,88 of the shaft 76 is oversized such thatthe ends 80,88 cannot fit through the connectors 82,90. In oneembodiment, the ends 80,88 have a spherical shape, cubic shape, etc.,though the ends 80,88 are not limited to any specific type of shape. Inyet another embodiment, the end 80 includes at least one depression slot96 disposed therein for engaging the pin elements 84. The depressionslot 96 can be disposed on the side of each end 80,88 of the shaft 76.The pins 84 can be elongated and extend past the first end 80 of theshaft 76 and engage holes 98 disposed in the socket element 78. The pinelements 84 engage the depression slots 96 and force the shaft 76 toturn as the rotor 36 turns the socket element 78. The elongated pinelements 84 and the depression slots 96 permit the shaft 76 to be easilyremoved from the socket element 78 to repair various portions of thedrive shaft assembly 20.

Similarly, the end 88 includes at least one depression slot 100 disposedtherein for engaging the second pin elements 92. The pins 92 can beelongated and extend past the second end 88 of the shaft 76 and engageholes 102 disposed in the passageway housing 24. The second pin elements92 engage the depression slots 100 and force the passageway housing 24to turn as the rotor 36 ultimately turns the shaft 76. The elongatedsecond pin elements 92 and the depression slots 100 permit the shaft 76to be easily removed from the passageway housing 24 to repair variousportions of the drive shaft assembly 20.

In another embodiment shown in FIG. 5, the socket element 78 can have anextension element 99 protruding from a central area to mate with anopening 101 disposed in the first end 80 of the shaft 76.

In a further embodiment, the connectors 82 and 90 can be constructed ofmultiple parts. For example, the connectors 82,90 can each have a firstpiece and a second piece that are connectable around the shaft 76 oncethe first end 80 and the second end 88 of the shaft 76 is disposed inthe socket element 78 and the passageway housing 24, respectively. Theconnectors 82,90 being constructed of multiple parts permits the ends80,88 of the shaft 76 to be oversized and permits easy access to theshaft 76 and other components of the drive shaft assembly 20 for repair.Thus, the ends 80,88 can be set in the socket element 78 and thepassageway housing 24, respectively, and the connectors 82,90 disposedaround the shaft 76. In one embodiment, each connector 82,90 isconstructed of two pieces and includes at least one opening 103 disposedtherein to allow access to the drive shaft assembly 20 for assembly anddisassembly.

The connector 82 can also be threaded on each end to engage the socketelement 78 and the retaining element 86. Similarly, the connector 90 canbe threaded on each end to engage the passageway housing 24 and thesecond retaining element 94. The drive shaft assembly 20 can alsoinclude at least one sealing element 104 disposed about the shaft 76. Inone embodiment, the sealing element 104 can be disposed around the shaft76 and inside of the connector 82. Similarly, another sealing element104 can be disposed around the shaft 76 and inside the connector 90.

In another embodiment shown in more detail in FIGS. 6 and 7, thelubrication fluid housing 42 includes at least one roller bearing 106disposed about a portion of the passageway housing 24 to facilitate therotation of the passageway housing 24 in the housing 16. The rollerbearing 106 can have at least one washer element 108 disposed adjacentto each side of the roller bearing 106. In one embodiment, the housing16 has a lip 110 extending inwardly therefrom for engaging one of thewasher elements 108. The passageway housing 24 can include a shoulder112 disposed on an outer portion 114 for engaging another washer element108 disposed on the other side of the roller bearing 106. It should beunderstood that the lubrication fluid housing 42 can include multipleroller bearings 106 disposed therein to facilitate in the rotation ofthe passageway housing 24 in the housing 16. In one exemplaryembodiment, a second roller bearing 106 is disposed on the other side ofthe lip 110 from the first roller bearing 106.

Each roller bearing 106 includes a roller cage 116 having a plurality ofbearing seats 118 for receiving a plurality of rollers 120. The bearingseats 118 are created by extension elements 122 extending from an innerring 124 of the roller cage 116. The extension elements 122 cooperatewith each extension element 122 disposed adjacent thereto to receive theroller 120. The rollers 120 can be maintained in the bearing seats 118by a retaining ring 126 that extends around the roller cage 116 andcontacts an outer edge 128 of the roller cage 116. The outer edge 128 ofthe roller cage 116 is made up of each outer edge 130 of each extensionelement 122. In one embodiment, the rollers 120 can be cylinder-shaped.

In another embodiment of the present disclosure, the retaining ring 126and the outer edge 128 of the roller cage 116 have a tapered interface131. The retaining ring 126 has an inner diameter, an outer diameter, afirst side 132 and a second side 134. To create the tapered interface131, the distance from the inner diameter to the outer diameter of theretaining ring 126 increases steadily from the first side 132 of theretaining ring 126 to the second side 134. Conversely, the distance fromthe inner ring 122 of the roller cage 116 to the outer edge 128 of theroller cage 116 decreases steadily from a first side 136 of the rollercage 116 to a second side 138 of the roller cage 116. The taperedinterface 131 permits the roller cage 116 to be removed from theretaining ring 126 to replace the rollers 124 and then put the rollercage 116 back into the retaining ring 126.

The roller cage 116, the rollers 124 and the retaining ring 126 have tobe designed and constructed of materials that can withstand the varyingoperating conditions in downhole environments. The rollers 124, rollercage 116, and retaining ring 126 can be constructed of any metallicmaterial known in the art that can withstand the temperature rangesfaced in downhole environments. In one example, the roller cage 116 canbe constructed of bronze and the retaining ring 126 can be constructedof a steel containing material.

From the above description, it is clear that the present disclosure iswell adapted to carry out the objectives and to attain the advantagesmentioned herein as well as those inherent in the disclosure. Whilepresently preferred embodiments have been described herein, it will beunderstood that numerous changes may be made which will readily suggestthemselves to those skilled in the art and which are accomplished withinthe spirit of the disclosure and claims.

What is claimed is:
 1. A method, the method comprising: deploying a mudmotor in a wellbore deploying a mud motor in a wellbore, the mud motorcomprising: an outer housing having an upper portion and a lowerportion; a power section disposed within the housing for rotating apassageway housing in response to fluid flow through the power section;a passageway disposed in the passageway housing where a small fluidvolume is disposed in a small annulus area created between thepassageway housing and the outer housing; a bearing assembly forfacilitating the rotation of the passageway housing; and a hydraulicapparatus for balancing a pressure drop experienced across the bearingassembly due to frictional flow of fluid through the passageway, thehydraulic apparatus having a port radially directed in the passagewayhousing in fluid communication with the passageway and the small annulusarea; flowing fluid through the mud motor to produce a rotary outputfrom the mud motor; and maintaining substantially balanced pressureacross sealing elements of a bearing assembly.
 2. The method of claim 1wherein the hydraulic apparatus further includes a nozzle disposed inthe passageway.
 3. The method of claim 2 wherein the hydraulic apparatusfurther includes a diffusing element disposed in the passageway andadjacent to the nozzle.
 4. The method of claim 3 wherein the nozzleincludes an annulus disposed thereabout, the annulus in fluidcommunication with the port on the side opposite from the small annulusarea.
 5. The method of claim 1 wherein the mud motor includes a fluidpassage disposed in a lower portion of the passageway housing, the fluidpassage in fluid communication with a downhole side of the bearingassembly.
 6. The method of claim 1 wherein the bearing assembly includesa lubrication fluid housing, a first sealing element and a secondsealing element to prevent drilling fluid from contaminating lubricationfluid in the lubrication fluid housing and lubrication fluid fromleaking out of the lubrication fluid housing.
 7. A method, the methodcomprising: deploying a mud motor in a wellbore, the mud motorcomprising: a power section disposed within a housing for rotating apassageway housing, the power section having a rotor; and a drive shaftassembly, the drive shaft assembly comprising: a shaft having a firstend and a second end for transferring rotation of the rotor to thepassageway housing, the first end having a plurality of depression slotsdisposed thereon; a socket element supported by the rotor and adapted toreceive the first end of the shaft, the socket element having aplurality of axially disposed holes therein; and a plurality ofelongated pins, each pin having a first end and a second end, the firstend of the elongated pins extend axially beyond the first end of theshaft and are disposed within the axially disposed holes in the socketelement and the second end of the elongated pins engaging the depressionslots disposed on the first end of the shaft; and flowing fluid throughthe mud motor to produce a rotary output from the mud motor.
 8. Themethod of claim 7 wherein the drive shaft assembly further comprises aconnector disposed around the shaft and threadably connected to thesocket element to prevent the shaft from leaving the socket element. 9.The method of claim 8 wherein the connector is comprised of two parts.10. The method of claim 8 wherein the drive shaft assembly furtherincludes a retaining element attachable to the opposite side of theconnector from the socket element.
 11. The method of claim 7 wherein thesocket element includes an extension element protruding from a centralarea of the socket element to engage with an opening disposed in thefirst end of the shaft.
 12. The method of claim 7 wherein the at leastone elongated pin is a cylinder.
 13. A method, the method comprising:deploying a mud motor in a wellbore, the mud motor comprising: a rollerbearing, the roller bearing comprising: a roller cage having an innerring, a plurality of extension elements extending therefrom and an outeredge, each pair of adjacent extension elements cooperating to form aplurality of bearing seats; a plurality of rollers disposed in eachbearing seat; and a retaining ring disposed around the outer edge of theroller cage to maintain the rollers in the bearing seats, the retainingring and the outer edge of the roller cage having a tapered interfacefrom a first side of the retaining ring and the roller cage to a secondside of the retaining ring and the roller cage; and flowing fluidthrough the mud motor to produce a rotary output from the mud motor. 14.The method of claim 13 wherein the distance from an inner diameter andan outer diameter of the retaining ring increases from the first side ofthe retaining ring to the second side of the retaining ring.
 15. Themethod of claim 13 wherein the distance from the inner ring to the outeredge of the roller cage decreases from the first side of the roller cageto the second side of the roller cage.
 16. The method of claim 13wherein the rollers are cylindrically shaped.